Tens of thousands of police officers could take to the streets in protest over a morale-sapping pay review that would leave at least two in five officers out of pocket, their union has warned.

Rank-and-file officers will do "everything possible" to vent anger over the measures which would leave forces in a position "worse than the 1970s", the Police Federation said.

But former rail regulator Tom Winsor said the most wide-ranging analysis of police pay in 30 years showed more than £1 billion of savings should be made, with most of this being redistributed from officers with comfortable back-office jobs to those on the front line.

The recommendations, which came as the Association of Chief Police Officers (Acpo) said 28,000 police jobs could be lost over the next four years, would leave at least 40% of officers worse off, with the biggest losers having their take-home pay slashed by up to £4,000 a year.

But Mr Winsor found that officers were "comparatively well paid", earning 10% to 15% higher than some other emergency workers and up to 60% higher than the average local earnings in regions such as Wales and the North East.

The system is in need of reform to recognise the "hardest jobs done in the most demanding circumstances", he said.

Only 57% of officers regularly work unsocial hours, and it is those who should be rewarded, he said.

Home Secretary Theresa May warned reductions are "unavoidable" amid efforts to minimise frontline job losses, but the Police Federation accused her of undervaluing rank-and-file officers who have faced a series of challenges in recent months.

Government cuts of 20% to police budgets, the potential loss of tens of thousands of officers, and plans to replace police authorities with locally elected police and crime commissioners from next year have all faced fierce opposition.

Officers are also expecting to be hit in the pocket by Thursday's review of public sector pensions by former Labour minister Lord Hutton.